1. Field of the Invention
This invention relates to the field of fiber optics and more specifically to the field of fiber optic connectors.
2. Description of the Prior Art
Fiber optic connector systems provide the means so that light can propagate through separable connections. To accomplish this, the connector system must align, hold connectors interconnect segments of fiber or connect fiber to active or passive devices. A fiber optic connector must control and minimize the loss of light energy as measured by the dB insertion loss. Many applications require insertion losses to be no more than in the range of about 1 dB. This requirement forces very stringent tolerances on the mechanical components of the connector system.
The prior art shows many connector designs. These include V-groove, three-rod containment, resilient ferrule, elastomeric bushing, jewel bushing, conical nose/conical adapter, and precision ferrule/precision adapter devices. In the ferrule types of connectors, a ferrule terminates the end of each optical fiber. For example, U.S. Pat. No. 4,645,296 discloses a resilient ferrule connector. U.S. Pat. No. 4,934,785 discloses a precision ferrule connector.
Currently, the major commercial connectors employ ferrules. These include the SMA, ST and FC connectors where each ferrule
is a right cylinder. These also include the Biconic connector where the ferrule is a truncated cone. Ferrule-terminated fibers require an alignment means to provide precise positioning of the fiber ends. In one design, an elastomeric sleeve aligns the front portions, termini, of the mating ferrules. In another design, a split spring sleeve aligns oppositely facing ferrules. In these designs, the ferrule diameter is slightly larger than the free-standing diameter of the alignment means. This insures interference for the precise alignment of the two mating ferrules. In yet another design, a precise bore provides a cylindrical channel for alignment.
In these major commercial connector systems, a separate, stand-alone component provides the alignment means. This component has several different names including adapter, alignment sleeve, coupling bushing and coupler.
The functions of fiber optic adapters are to secure, position and align mating pairs of connectors thereby supporting reliable circuits. In the major commercial connector systems, adapters use cylindrical (or conical) geometries to achieve the critical positioning of the mating fiber optic connectors. Adapters require precise mechanical tolerances. The techniques to achieve these tolerances are both difficult and expensive. The details of the adapter design depends on the specific connector type.
The adapter should permit multiple connect-disconnect cycles without damage to the connector system components. In addition, the insertion loss values should be roughly constant when mated throughout the connect-disconnect cycles.
Most adapters can secure the fiber optic connectors to prevent their accidental removal when the connectors experience forces or tensions. Several means are in common use. The most popular of these include threaded nut and bayonet nut.
Some adapters attach to a bulkhead. Some adapters have an exterior thread and use a pair of opposed nuts to secure the adapter to a bulkhead. Alternatively, some adapters use a nut pressing against a fixed land on the adapter body. Other adapters provide tapped holes to receive bolts through the bulkhead.
U.S. Pat. No. 4,186,997 and U.S. Pat. No. 4,526,431 disclose additional adapters.
At present, a popular connector for fiber optic systems is the SMA connector. (SMA is the registered trademark of Amphenol Corporation.) This connector is the basis for a military specification, MIL-C-83522. In that specification, the adapter is shown as a machined part made from steel. That specification requires tolerances as tight as 0.0003 inch. Maintaining such tight tolerances on machined metal parts has resulted in expensive parts that are difficult to manufacture. Even with such tight tolerances, adequate performance with the most popular fiber sizes requires the introduction of an additional part. This additional part is a plastic sleeve having the form of a right circular tube. The combination of a machined metal part and a plastic sleeve creates practical adapters. These adapters succeed in interconnecting the most popular fiber types, including 50/125, 62.5/125 and 100/140 (the numbers referring to the core and fiber diameters in microns).
Another connector for fiber optic systems is the FC connector. This connector satisfies selected telecommunication applications. It also finds applications with single mode optical fiber where the smaller core size of about 8 microns demands even more stringent dimensional tolerances. With this FC system, the adapter consists of several metal pieces and a very critical ceramic sleeve. The ceramic sleeve, a split-ring right circular tube, requires tight tolerances, on the order of microns. The ceramic sleeve with its tight tolerances assures the required positioning and alignment of the connector tips. The additional metal pieces protect the ceramic sleeve and secure the connectors. This ceramic sleeve has been a very difficult part to manufacture. Only a few vendors in the world now own the required technology. Hence, the sleeve continues to be a very costly part.
Yet another connector for fiber optic systems is the ST connector. (ST is a trademark of AT&T Corporation.) This connector finds application primarily with multimode fibers but may have the potential to satisfy additional applications with single mode fiber. This connector system includes more than one type of adapter. In one ST adapter design, metal parts capture a split alignment sleeve. Maintaining the required manufacturing operations has led to difficulties and costly parts. In another ST adapter design, plastic molded parts capture a ceramic sleeve. Again, the manufacture of the ceramic sleeve with its required precise tolerances has led to production limitations and difficulties as well as expensive parts.